1. Field of the Invention
The present invention relates to the field of photodetector array devices. More particularly, methods are provided for placing arrays of spectroscopic filter material on photodetector arrays such as image sensors and focal plane arrays.
2. Background of the Invention
Compact, low-cost digital imaging systems that combine the benefits of high spatial and spectral resolution are in demand for the next generation of analytical and surveillance instruments. Advances in commercial image sensors (“camera chips”) and infrared focal plane arrays have led to picture element (“pixel”) densities with very high spatial resolution. Despite pixel densities sufficient to resolve ultrafine features with large fields of view, commercially available color CMOS and CCD cameras are still limited in the degree of spectral (chromatic) resolution. Likewise, spectroscopic imaging outside the visible spectrum, either in the ultraviolet or the infrared is rarely accomplished at the photodetector level. Instead, spectral resolution of color imaging systems is generally restricted to the Bayer red-green-blue (RGB) color filter array (CFA) mosaic pattern found on virtually all color image cameras. These color cameras are designed to meet minimal color reproduction requirements for digital photography, but are in no way optimum, for example, in bioanalytical instrumentation used to perform medical or scientific analyses. In typical instrumentation, more precise definition of spectral bands is achieved with a combination of a gray-level monochrome image sensor and one or more dispersive or absorptive filter elements that are bulky and expensive, particularly when motorized switching between filter sets is employed. Likewise, electronically-tunable filters (e.g. LCD, acousto-optic, Fabry-Perot, etc.) reduce image acquisition speed and do not yield high spectral fidelity or efficient light throughput. Elimination of external dispersive elements and slow tunable filters requires directly integrating higher spectral definition into the mosaic pattern on the surface of the photodetector array, which may be silicon CMOS/CCD in the ultraviolet and visible spectral range, InGaAs in the near infrared radiation (NIR) range and short wave infrared radiation (SWIR) range, InSb in the mid wave infrared radiation (MWIR) range and HgCdTe in the long-wave, or far infrared radiation (LWIR) range. The photodetector array may not be an array of photodiode pixels and may consist of arrays of bolometer or pyroelectric detectors, for example. In addition, the photodetector array may be a structured ensemble or layered arrangement of discrete detectors or photodetector arrays, perhaps sensitive to wavelengths in a variety of spectral bands.
What is needed is a process for expanding the number of detected spectral intervals, and increasing spectral resolution, spectral range, and sensitivity dynamic range of photodetector arrays through batch assembly of filter arrays directly on the surface of the photodetector array, or onto a substrate or stamp that can be either applied to or used to transfer the filter array to the photodetector array surface.